DAWN, ENCELADUS, DUST AND PLUTO

Many exciting things are happening in astronomy. Here are just a few.

Dawn is Under the Microscope

Dawn has been getting a check up since its launch on September 27. Members of NASA's Dawn mission control team have been sending commands and checking out spacecraft systems. The first test firing of one of Dawn's three ion engines began Saturday, October 6 and ran for 27 hours as the team evaluated the engine at five different throttle levels ranging from flight idle through full throttle. The test consumed less than .28 kilograms (10 ounces) of the spacecraft's xenon fuel supply -- less than the contents of a can of soda. Dawn's fuel tank carries 425 kilograms (937 pounds) of xenon propellant. Over their lifetime, Dawn's three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) -- a record for spacecraft. Good engine performance is vital to the success of Dawn's 8-year, 4.9 billion-kilometer (3-billion-mile) journey.

The team will test Dawn for two more months before they consider the spacecraft mission operational. Dawn will begin its exploration of asteroid Vesta in 2011 and the dwarf planet Ceres in 2015. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's science instrument suite will measure shape, surface topography, tectonic history, elemental and mineral composition, and will seek out water-bearing minerals. In addition, the team will measure the masses and gravity fields of Vesta and Ceres by monitoring how the Dawn spacecraft orbits the two bodies. For more on Dawn, check out the mission home page: http://dawn.jpl.nasa.gov/ .

Enceladus Jets are Better Understood

A recent analysis of images from NASA's Cassini spacecraft gave conclusive evidence that the observed jets of fine, icy particles spraying from Saturn's moon Enceladus originate from the hottest spots on the moon's "tiger stripe" fractures that straddle the moon's south polar region. The new results were published in the October 11, 2007, issue of the journal Nature.

Since the first images of the Enceladus jets were taken in 2005, imaging scientists suspected these jets, which collectively feed a plume that towers thousands of kilometers, or miles, above the moon, had been coming from the tiger stripes. But this work provides the first conclusive proof, as well as confirming a relationship between the jets and the unusual heat radiating from the fractures.

The scientists also suggest that the character of the jets may change depending on tidal frictional heating within the fractures and its variation over length of the moon's orbit around Saturn. However, more work remains to determine this.

The imaging team was the first of many to suggest that the jets may erupt from pockets of liquid water. This notion, combined with the unusually warm temperatures and the organic material detected in the vapor accompanying the icy particles, lead to the scientist to include Enceladus as one of the Saturnian moons that may contain a habitable zone for life. The next opportunity to learn more will come when Cassini flies through the plumes in March 2008, obtaining additional data about its chemical composition and the nature of its jets.

For more on Enceladus and the rest of the Saturn system, check out the mission home page: http://www.nasa.gov/cassini . You can find great information and graphics at these websites:http://saturn.jpl.nasa.gov/ , http://www.nasa.gov/cassini and http://ciclops.org/ .

Dust from Black Holes

New findings from NASA's Spitzer Space Telescope suggest that space dust – the same stuff that makes up living creatures and planets – was manufactured in large quantities in the winds of black holes that populated our early universe. The details will be published in an upcoming issue of the Astrophysical Journal Letters. The lead author is Ciska Markwick-Kemper of the University of Manchester, U.K.

Space dust is essential to the formation of planets, stars, galaxies and even life as we know it. The dust in our corner of the universe came from dying stars that were once a lot like our sun. But, when the universe was less than a tenth of its present age of 13.7 billion years, sun-like stars hadn't been around long enough to die and make dust. So what was making the dust when the universe was young?

Many have long thought that short-lived, massive exploding stars, or supernovae, might be the source, while others have suggested that a type of energetic, growing supermassive black hole, called a quasar, could be a contributing factor. A quasar consists of a supermassive black hole surrounded by a dusty doughnut-shaped cloud that feeds it. Theoretically, dust could form in the outer portion of the winds that slowly blow away from this doughnut cloud.

Markwick-Kemper and her team decided to test the quasar theory by investigating a quasar, called PG2112+059, located in the center of a galaxy about 8 billion light-years way. They found a mix of the ingredients that make up glass, sand, marble and even rubies and sapphires. While the mineral constituting glass was expected, the minerals for sand, marble and rubies were a surprise. Why? These minerals are not typically detected floating around galaxies, suggesting they could have been freshly formed in the winds rushing away from the quasar.

For instance, the ingredient that makes up sand, crystalline silicate, doesn't survive for long free-floating in space. Radiation from stars zaps the minerals back to an amorphous, glass-like state. The presence of crystalline silicate therefore suggests something – possibly the quasars winds – is churning out the newly made substance. For graphics and more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .

Pluto Family Portrait

On October 12, astronomers announced that new images taken of the Pluto system are the sharpest ever made and 20 times brighter than those taken 30 years ago when Pluto’s large moon Charon was discovered. The images are expected to bring astronomers closer to estimating the sizes of Pluto's satellites, Nix, Hydra and Charon.

The images were taken by astronomer David Tholen using one of Mauna Kea’s twin Keck telescopes, and utilizing the Keck’s adaptive optics system in order to compensate for turbulence in Earth’s atmosphere. The work was done in early September, when Pluto was at its maximum brightness. Tholen took 16 images and combined them into a single picture.

The moons Nix and Hydra, discovered in 2005 with the Hubble Space Telescope, are currently estimated to be less than 62 miles in diameter. The moon Charon is estimated to be 753 miles (1,212 kilometers) and Pluto is estimated to be 1,429 miles. Many more images of the Pluto system will be taken over the next several lunar orbits around Pluto. This will allow astronomers to determine precise positions of the satellites, and thereby determine precise masses for Nix and Hydra.

The more definitive measurements are important for scientists planning the 2015 flyby of Pluto with NASA's New Horizons spacecraft. One of the current astronomy goals is to determine the proper exposure times for the New Horizons instruments before their arrival. To learn more about the New Horizons mission to Pluto and the Kuiper belt, check out the mission hope page: http://pluto.jhuapl.edu/

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THE SKY THIS WEEK

Here are some observing highlights for the week. These events are given from the perspective of observers in the northern hemisphere. No offence to southern-hemisphere folks, it's just because of where I live.

Oct 15, After Sunset - Moon, the planet Jupiter and the star Antares appear very close together.

Oct 19, 4:33 am EDT - first-quarter Moon

Oct 21 – Peak of the Orionid Meteor Shower. This shower is caused by dust from Halley's Comet, which is also responsible for the Eta Aquarid Shower in the spring. Meteors from the Orionid shower may be visible throughout the month of October and through the first week of November. The maximum will probably last from the 19th through the 23rd, with the peak around the 22nd. At its height the shower should produce 15 to 20 meteors per hour. The meteors will appear to originate from a point in the sky between the constellations Gemini and Orion, high in the southern sky during the October evenings.

Meteors are best viewed from a dark-sky location. Observers in for the duration of the evening, or at least for several hours, should bring along a few things: a sleeping bag or blankets for warmth, a recliner or lawn chair, a hot beverage to help cut the chill, and binoculars to view the smoke trails of just-past meteors.

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THIS WEEK IN HISTORY

Oct 15, 1997 - Cassini launch (10th anniversary). Ten years ago, a Titan IV rocket launched the Cassini spacecraft on its mission to Saturn. To learn about the work currently don by Cassini, visit the NASA Saturn home page: http://saturn.jpl.nasa.gov/

Oct 18, 1967 - Venera 4, Venus Landing (40th Anniversary). The Soviet spacecraft Venera 4 (Venus 4) launched June 12, 1967 (UTC) with an announced mission to study the Venusian atmosphere. On October 18, 1967, the spacecraft entered the Venusian atmosphere and released two thermometers, a barometer, a radio altimeter, and atmospheric density gauge, 11 gas analyzers, and two radio transmitters operating in the DM waveband. The main bus, which had carried the capsule to Venus, carried a magnetometer, cosmic ray detectors, hydrogen and oxygen indicators, and charged particle traps. The spacecraft braked and then deployed a parachute system after entering the Venusian atmosphere. Signals were returned by the spacecraft until it reached an altitude of 24.96 km.

Oct 19, 1967 - Mariner 5, Venus Flyby (40th Anniversary). The NASA spacecraft Mariner 5 (also called Mariner Venus ’67) was launched June 14, 1967 (UTC). Mariner 5 was a refurbished backup spacecraft for the Mariner 4 mission and was converted from a Mars mission to a Venus mission. The spacecraft was fully attitude stabilized, using the sun and Canopus as references. A central computer and sequencer subsystem supplied timing sequences and computing services for other spacecraft subsystems. The spacecraft passed 4,000 km from Venus on October 19, 1967. The spacecraft instruments measured both interplanetary and Venusian magnetic fields, charged particles, and plasmas, as well as the radio refractivity and UV emissions of the Venusian atmosphere.

Oct 20, 1632 - Birth of Christopher Wren (375th Birthday). Sir Christopher Wren, born Oct. 20, 1632, East Knoyle, Wiltshire, England, died Feb. 25, 1723, London. Designer, astronomer, geometrician, and the greatest English architect of his time. Wren designed 53 London churches, including St. Paul's Cathedral, as well as many secular buildings of note. He was a founder of the Royal Society (president 1680–82), and his scientific work was highly regarded by Sir Isaac Newton and Blaise Pascal. He was knighted in 1673.

Oct 21, 1897 - Opening of Yerkes Observatory (110th Birthday). Yerkes Observatory is a facility of the Department of Astronomy and Astrophysics of the University of Chicago. It was established in 1897 on Geneva Lake in Williams Bay, Wisconsin. Until the mid-1960's, Yerkes Observatory housed all of the Department's activities. Today the 77-acre, park-like site in southeast Wisconsin provides laboratory space and access to telescopes for research and instruction. The telescopes at Yerkes include the 40-inch (102 cm) refractor constructed by Alvan Clark and Sons (the largest refractor), a 40-inch (102 cm) reflector, a 24-inch (61 cm) reflector, a 10-inch (25 cm) Cassegrain reflector, and a 7-inch (18 cm) Schmidt camera. To learn more, visit the Yerkes Observatory public home page: http://astro.uchicago.edu/yerkes/

The Yerkes Observatory and its grounds are in serious danger of being sold by the University of Chicago to local developers. To learn what is being done to help save the Yerkes Observatory, and to learn how you can help, visit the organization website, Save Yerkes Observatory: http://www.saveyerkes.com/

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MUSICAL DIVERSION: HEART OF OAK

Heart of Oak is an 18th century song of the sea. The tune was written by Dr. William Boyce (1711-1779). The English words were written by the famous actor David Garrick (1716-1779) in 1759. Garrick is also credited with the theatrical blessing, "Break a Leg" as he was reportedly so involved in his performance of Richard III that he did not notice the pain of a fracture he incurred.

There is also an American set of lyrics, called The Liberty Song.

Heart of Oak

Come cheer up, my lads! 'tis to glory we steer,
To add something more to this wonderful year;
To honour we call you, not press you like slaves,
For who are so free as the sons of the waves?

Chorus:

Heart of oak are our ships, heart of oak are our men;
We always are ready, steady, boys, steady!
We'll fight and we'll conquer again and again.
We ne'er see our foes but we wish them to stay,
They never see us but they wish us away;
If they run, why we follow, and run them ashore,
For if they won't fight us, we cannot do more.

(Chorus)

They swear they'll invade us, these terrible foes,
They frighten our women, our children, and beaus;
But should their flat bottoms in darkness get o'er,
Still Britons they'll find to receive them on shore.

(Chorus)

We'll still make them fear, and we'll still make them flee,
And drub 'em on shore, as we've drubb'd 'em at sea;
Then cheer up, my lads! with one heart let us sing:
Our soldiers, our sailors, our statesmen and Queen.

(Chorus)

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Many versions of these words have developed over the years. Fans of Walt Disney motion pictures may recall that actors Peter Ustinov, Dean Jones and Suzanne Pleshette sung a version in the 1968 Disney film "Blackbeard's Ghost." And fans of the science fiction television series "Star Trek: The Next Generation" may remember an episode from the third season, entitled "Alegience," in which another version was sung. Below is the first verse and the chorus sung in that episode.

Come, cheer up, my lads, 'tis to glory we steer,
To find something new in this wonderful year;
To honour we call you, as freemen not slaves,
For who are so free as the sons of the waves?

Chorus:

Heart of oak are our ships, jolly tars are our men,
we always are ready; Steady, boy, steady!
We'll fight and we'll conquer again and again!

In the above chorus, the word "tar" is a slag term that was used for a sailor. Their hats and clothes were treated with tar to waterproof them. The tar-impregnated cloth, or tarpaulin, provided protection in harsh conditions. Because of this, a sailor was called a "tarpaulin," or "tar" for short. Fans of Gilbert and Sullivan may remember a song from the musical "HMS Pinafore" entitled "A British Tar."

To review the history, the text, or to listen to the melody, check out this page from the "Songs of the Sea" section of "Contemplations from the Marianas Trench - Music and Deep Thoughts" - http://www.contemplator.com/england/heartoak.html

To see a GIF image file of the score of the song, or to download an ABC file of the score, or other notations, visit this mirror site of Digital Tradition -http://sniff.numachi.com/pages/tiHEARTOAK;ttHEARTOAK.html

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